Rasch Measurement in language education Part 6:
Rasch Measurement and Factor Analysis
by James Sick (International Christian University, Tokyo)
[ p. 15 ]In fact, wide differences in item difficulty, or endorsability in the case of Likert style items, can be problematic for factor analysis. When an item is difficult to endorse, it may not correlate strongly with items that are easy to endorse, even if these items are indicative of the same trait. In some instances, easy items and difficult items may not load together, forming "difficulty" factors, a misleading result that is considered a nuisance by the factor analyst. Designing a questionnaire that works well with factor analysis thus requires that the survey designer avoid items that are either very easy or very difficult to endorse. The Rasch approach is not affected by this restriction, and in fact functions best when items vary in difficulty. From a Rasch perspective, a well-designed questionnaire employs items with a range of difficulty that matches the range of person measures in the target audience. Moreover, the hierarchical ranking of the items can be employed as an empirical test of the validity of the construct. If the items measure a single, coherent latent trait, the Rasch fit statistics should indicate that items fit the model. In addition, the ranking of the items should "makes sense" to the analyst qualitatively, in light of what is understood about the ability or construct being measured.
[ p. 16 ]
|Rasch Measurement in Language Education Series:|
|Article 1:||Article 2:||Article 3:||Article 4:||Article 5:||Article 6:|
[ p. 17 ]